Current Version of Parts Placement Guide
to print or download a
with dimensions, and see-thru view of coax routing.
2008 Version:--differed in location of C1-R1.
Kit Troubleshooting . . .
-- Common problems:
a) --Forgetting to install the wire "jumper"
b) --Forgetting or confusing a component: Use the photos inside the manual overleaf.
Click here to download a photo to help with
component placement, including placement of R1. NOTICE in the photo
how hard it can be to discern the red from orange color bars on the resistors!
c) --Solder bridges which accidentally connect two pads that are not supposed to be connected.
(Click here for a photo of a solder bridge, which also shows the Coax connections)
d) --Off-Axis Nulling or No Null at all:
With a known strong signal, if there is constant off-axis nulling or no null at all, check the continuity
from the antenna wire to a circuit point on the board foil using an Ohmmeter. Flat washers are manufactured by stamping, and thus have a slight
"cup" cross-section. Put the rounded side against the board foil. It was discovered that with the concave
side against the board pad, it is often very difficult to tighten the hardware enough to compress
the center of the washer so that it reliably contacts the board foil, which is sitting in a bit of a
depression caused by the surrounding "solder mask" coating.
Latest preferred method: Antennas are mounted on the Circuit Side of the board!
Put the screw through from the component side, then on the non-component side,
the washer with rounded side against the board foil pad, then the antenna eyelet, then the lockwasher, then the nut, and tighten.
The HANDI-Finder® is a HANdheld DIrection Finder
which can be used to localize both AM and FM carrier-based sources
using a single connection to the antenna input of an FM receiver tuned to the
frequency of interest in the range of 45 to 450 MHz.
It has been designed for bare-bone functionality as
well as low power consumption, simplicity, and economy!
Overall, it is a basic, inexpensive way to explore
the concept of electronic direction finding, and provides something
relatively compact to keep readily available for locating
sources of interference. It provides a convenient basis for further
experimentation by those who want to try more elaborate antenna arrays.
Soldering, general assembly skills, and patience ARE required, but it makes a great club project
for the basis of also teaching those valuable skills!
Fabrication can be straight-forward, but takes time. Overall, expect the process of unpacking,
checking the parts, and assembling the basic board with care, to take about two hours.
The subsequent steps can easily take longer than one might expect.
Two open-loop antennas (not supplied) are made from coat hanger wire or welding/brazing rod,
bent into halves of a "bow-tie" shape and mounted directly to the
foil side circuit board, as illustrated in the "layout" drawing.
The 50-Ohm coax downlead (not supplied) is connected to an FM receiver and detects
the carrier regardless of whether the transmission mode is AM or FM.
The unit is switched on (UP) and rotated for a null in the audio tone
that it ADDS to the audio coming out the receiver.
The signal direction is perpendicular to the
plane of the antennas. There is 180-degree ambiguity,
but this is not a problem in actual use because
multiple "bearings" must be taken anyway
in order to establish a "fix" on the location.
Once close in, the operator works toward the general
sense of the direction, and again the ambiguity is
not a problem.
The 3-position switch is moved DOWN to stop the tone
but still keeps the antenna activated for monitoring and standby purposes,
--or it is moved to the CENTER
position to shut off the unit. Refer to the extensive discussion
in the manual which describes construction variations, and the concepts behind the design.
Finally, a handle (not supplied) must be fabricated and added. This can be anything from a wooden paint
stirrer to a nicely molded paint roller handle, modified to attach to the flat circuit board, as partially seen in the photos.
"Build the HANDI-Finder" appeared as an article in QST Magazine, May, 1993.
All the information in that article and much more is included here!
By clicking on the appropriate boxes in this web page,
all the drawings and text that come with the kit can be printed out or downloaded from
PDF files. If you are unable to buy the kit, you can emulate the layout and build one on perfboard!
are available from sources like Digi-Key and Mouser.
It should be noted that this is an experimenter's kit that starts out simple, but can get more complex
as one expands on the principle to get better performance. Generically, this is known as a TDOA,
of this sort are susceptable
to multipath, which is often overwhelming!
This simple configuration can be quite acceptable on
lakes or flat open land.
in the vicinity of hills, buildings, or dense forest can be quite problematic due to multipath.
Here, a combination of techniques, such as using the circuit in combination with two spaced beam antennas,
can be much more effective, but also much more bulky! Also note that since this scheme detects a carrier-based
signal source, it CANNOT be used to localize random noise sources!
HANDI-Finder® Experimenter's Kits
may be obtained by contacting:
Northern Ohio Amateur Radio Development
P. O. Box 271
Brunswick, OH 44212-0271 USA
Tel: 330-225-7373, Rick, K8SCI
for prices and order info.
Sales are limited to the US and Canada only.
Unfortunately, due to outrageous shipping costs,
we have to require an ADDED charge for Canada.
Only complete packaged kits may be ordered.
Problems with defective or missing parts
are promptly addressed.